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iris_raj
05-02-2006, 04:54 AM
Today I tired to experiment with glMultMatrix for rendering a simple cube.Initially My I focuseed by viewing position using gluLookAt.Later I changed it using glMultMatrix by specify 4x4 matrix. Now cube is partially clipped. Why is it so. I have not changed projection values. Below is code.


#include <GL/glut.h>
#include <GL/gl.h>
#include <stdlib.h>
#include <math.h>

#define PI 22/7

float theta=90*PI/180;
GLfloat T[16]={1,0,0,0,0,1,0,0,0,0,-5.0,0,0,0,0,1};

void init(void)
{
glClearColor (0.0, 0.0, 0.0, 0.0);
glShadeModel (GL_FLAT);
}


void display(void)
{
glClear (GL_COLOR_BUFFER_BIT);
glColor3f (1.0, 1.0, 1.0);
glLoadIdentity (); /* clear the matrix */
/* viewing transformation */
//gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glMultMatrixf(T);
//glScalef (1.0, 2.0, 1.0); /* modeling transformation */
glutWireCube (1.0);
glFlush ();
}

void reshape (int w, int h)
{
glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
glFrustum (-1.0, 1.0, -1.0, 1.0, 1.5, 20.0);
glMatrixMode (GL_MODELVIEW);
}

void keyboard(unsigned char key, int x, int y)
{
switch (key) {
case 27:
exit(0);
break;
}
}

int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize (500, 500);
glutInitWindowPosition (100, 100);
glutCreateWindow (argv[0]);
init ();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutKeyboardFunc(keyboard);
glutMainLoop();
return 0;
}

RigidBody
05-02-2006, 07:04 AM
maybe it's because your matrix scales the z-coordinate by a factor of -5.0.

jide
05-02-2006, 07:32 AM
Yes what you might have wanted to do is to translate not scale:


GLfloat T[16]=
{
1,0,0,0,
0,1,0,0,
0,0,1,0,
0,0,-5,1
};

iris_raj
05-02-2006, 11:42 PM
Thanks. Now it is fully visible.But again,it losts it projection character. I want the viewing volume to be a Frustum. But Output I am getting looks as if viewing volume an orthographic one.

Kindly respond

Rajesh.R
IRIS,CAIR
Bangalore - 1

jide
05-03-2006, 04:05 AM
A call to glFrustum always creates a perspective not an orthographic view. Maybe it's because what's you see hasn't got much depth so the perspective isn't 'seenable'. Try gluPerspective instead or draw more deep objects.